1. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 1 On L-SIG TXOP Protection Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at.http:// ieee802.org/guides/bylaws/sb-bylaws.pdfstuart.kerry@philips.compatcom@ieee.org Date: 2006-07-11 Authors:

2. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 2 Summary of L-SIG TXOP Protection Related Comments L-SIG TXOP protection related comments ID (CID 3765, 8277, 7258, 6788) : –C1: L-SIG TXOP shouldnt be used under mixed legacy-HT BSS. –C2: L-SIG TXOP shouldnt be used under overlapping BSS, –C3: NAV be set by L-SIG only when HT-SIG CRC pass. –C4: Applying HT-SIG CRC to cover L-SIG so to enhance L-SIG TXOP protection.

3. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 3 Outline of this Presentation Provide an analytical framework for the problem. Discussions and conclusions.

4. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 4 Assumptions of the Analytical Framework CCA detection: there are three types of CCA detection, namely positive CCA (packets exist with positive detection), miss CCA (packets exist but miss detection) and false CCA (packets not exist but positive detection). We assume miss CCA will always incur false CCA (most likely in reality). Assume bit error rate of L-SIG and HT-SIG are all Pb_sig and independent bit-wise. We will study Pb_sig = from ~0.5 to 10^-6. Independent comes from interleaver. (That is iid) Assume 1T1R AWGN. 8 bits HT-SIG CRC: 1. Assume all 8 bits errors can not be detected by CRC. Assume coding gain of 64 state rate ½ BCC is 7dB (without deducting rate reduction loss.)

5. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 5 Definition of Key Parameters Pb_sig: Bit error rate of L-SIG and HT-SIG Ps_lsig: Symbol error rate of L-SIG. Pfa_lsig: False alarm rate of L-SIG. (related to C1) Ps_sig: Symbol error rate of HT-SIG. Pfa_lsig2: False alarm rate of L-SIG with HT-SIG CRC pass. (related to C3) Pfa_htsig: False alarm rate of HT-SIG. Ps_sig2: Symbol error rate of HT-SIG with CRC cover L-SIG. Pfa_htsig2: False alarm rate of HT-SIG with CRC cover L-SIG. (related to C4) Pe_1000B: Packet error rate of 1000 byte packets with the same modulation and coding as L-SIG.

6. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 6 Equations of Key Parameters Pb_sig = from ~0.5 to 10^-6 Ps_lsig = 1- Pb_sig^24 Pfa_lsig = n =2:2:24} C n 24 *Pb_sig^n Ps_sig = 1- Pb_sig^48 Pfa_htsig = 1/256* n =9:48} C n 48 * Pb_sig^n Pfa_lsig2 = Pfa_lsig * (Pb_sig^48+ Pfa_htsig); Ps_sig2 = 1- Pb_sig^72 Pfa_htsig2 =1/256* n =9:72} C n 72 * Pb_sig^n Pe_1000B = 1- Pb_sig^8000.

7. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 7 Error Probabilities vs. BER

8. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 8 Converting BER to SNR SNR_uncoded = 20*log10(erf -1 (1-Pb_sig)) (dB) SNR = SNR_uncoded + 7 (dB)

9. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 9 Error Probabilities vs. SNR

10. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 10 General Discussions The analytical curves show us the first time of whole picture, instead of just one particular point. The figures cover two important regions, The higher SNR region dictates the performance of positive CCA. The lower SNR region dictates the performance of false CCA. Red curve is the performance of legacy device and 11n draft. Magenta curve is the performance suggested by C3. Green curve is the performance suggested by C4. Red Curve has the worse performance. There is a crossing over point between magenta and green curves. Green curve has the best performance under positive CCA. Magenta curve has the best performance under false CCA.

11. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 11 L-SIG TXOP under Positive CCA Even L-SIG protection along, false alarm rate is low under usable SNR: < 10^-3 with SNR 0dB. C3 doesnt really improve this region. C4 is doing very well in this region. Doesnt really show problem here! This is not where the real problem happens!

12. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 12 L-SIG TXOP under False CCA According to 802.11g standard positive CCA rate > 90% within starting 4us. The others are miss CCA and false CCA. Assume miss CCA will introduce false CCA, False CCA rate < 10%. False CCA can also be caused by co-channel (OBSS) or adjacent channel interference. Note that BER is approach 50%. False SIG rate for L-SIG protection is 50%! False SIG rate for C3 is 0.2% False SIG rate for C4 is 0.39% This is where the real problem with L-SIG protection!

13. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 13 C1 Discussion C1: L-SIG TXOP shouldnt be used under mixed legacy-HT BSS. –Under False CCA, L-SIG protection has 50% false SIG rate, this mechanism will kill legacy device under environment with significant co-channel or adjacent channel interference. –Even under clean environment with 10% false CCA rate, overall 5% (50%*10%) false SIG rate with random LENGTH field could be a problem! –It is important that we accept this comment, so that millions deployed legacy device wouldnt be at risk with this feature. –Suggest to accept it.

14. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 14 C3 Discussion C3: NAV be set by L-SIG only when HT-SIG CRC pass. –Best performance of proposed method under false CCA. It is also important that it requires change only inside L-SIG TXOP, not other parts of spec. –Need to improve the region between positive CCA and false CCA. –Suggest to accept. –This conclusion is inline with Intels analysis.

15. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 15 C4 Discussion C4: Applying HT-SIG CRC to cover L-SIG so to enhance L-SIG TXOP protection. –Improve performance at both false CCA and positive CCA regions. –However compared to C3, this method require change that will affect design outside L-SIG TXOP which is neither necessary nor desirable. –Suggest to reject it. –This conclusion is inline with Intels analysis.

16. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 16 Summaries of Suggested Resolution C1: L-SIG TXOP shouldnt be used under mixed legacy-HT BSS. –Accept. See slide 13 for detail. C2: L-SIG TXOP shouldnt be used under overlapping BSS, –Accept. Similar to C1. C3: NAV be set by L-SIG only when HT-SIG CRC pass. –Accept. See slide 14 for detail. C4: Applying HT-SIG CRC to cover L-SIG so to enhance L-SIG TXOP protection. –Reject. Major change with similar performance under key false CCA condition as compared to C3. See slide 15 for detail.

17. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 17 Four Possible Approaches Remove L-SIG TXOP protection completely –Given the minor potential benefit of L-SIG TXOP protection with several known induced difficulties, the potential benefit is doubtable. This is most clean way to resolve all sort of L-SIG TXOP issues. Extended HT-SIG CRC to cover L-SIG and forbid L-SIG TXOP under mixed legacy HT BSS. –This is a clean solution too, but will need to change core spec. (even though a little one). Shall we change a core mandatory spec because of an optional feature? Honor L-SIG only when HT-SIG CRC pass. with RSSI threshold gating and forbid L-SIG TXOP under mixed legacy HT BSS. –This will works. The best compromise. Honor L-SIG only when HT-SIG CRC pass. –This approach along is not enough.

18. doc.: IEEE 802.11-06/0909r0 Submission July 2006 David Tung, RalinkSlide 18 Straw Poll Remove L-SIG TXOP protection completely Extended HT-SIG CRC to cover L-SIG and forbid L- SIG TXOP under mixed legacy HT BSS. Honor L-SIG only when HT-SIG CRC pass. with RSSI threshold gating and forbid L-SIG TXOP under mixed legacy HT BSS. Honor L-SIG only when HT-SIG CRC pass.